<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>使用计时事件制作的钟表</title>
    <script>
        function startTime() {
            var today = new Date();
            var h = today.getHours();
            var m = today.getMinutes();
            var s = today.getSeconds(); // 在小于10的数字前加一个‘0’
            m = checkTime(m);
            s = checkTime(s);
            document.getElementById('txt').innerHTML = h + ":" + m + ":" + s;
            t = setTimeout(function () { startTime() }, 500);
        }
        function checkTime(i) {
            if (i < 10) {
                i = "0" + i;
            }
            return i;
        }
    </script>
</head>

<body onload="startTime()">
    <div id="txt"></div>
</body>

</html>